The present invention relates generally to the field of magnetic data storage and retrieval systems. More particularly, the present invention relates to a transducing head having a perpendicular writer portion in which side-writing is reduced significantly as compared to existing transducing head designs.
A transducing head of a magnetic data storage and retrieval system typically includes a writer portion for storing magnetically-encoded data on a magnetic medium and a reader portion for retrieving the magnetically-encoded data stored on the magnetic medium. The reader portion is positioned adjacent the writer portion. The writer portion may be a perpendicular writer or a longitudinal writer. In either case, the general structure of the writer is similar, although the actual operation and dimensions of its elements will differ substantially. In a longitudinal writer, the poles are commonly referred to as a bottom pole and a top pole, whereas in a perpendicular writer, the poles are commonly referred to as a return pole and a main pole. Longitudinal writing differs from perpendicular writing in that bits are written to a magnetic medium in a direction substantially parallel to a surface of the magnetic medium, rather than in a direction substantially normal to the surface of the medium. Perpendicular writers are utilized in order to obtain higher areal density.
A perpendicular writer is typically formed of a main pole, a back via, a return pole, a write gap, and one or more conductive coil layers. A main pole may also be known as a “write pole,” and a return pole may also be known as an “auxiliary pole.” The main pole and return pole are separated from each other at an air bearing surface (ABS) of the perpendicular writer portion by the write gap and are connected to each other at a region away from the ABS by the back via. The ABS is the surface of the transducing head immediately adjacent a magnetic medium. Positioned between the main pole and the return pole are the conductive coil layers encapsulated by insulating layers, which generally wrap around the back via. The main pole, back via, and return pole are each made of magnetic material. The write gap is generally a layer formed of nonmagnetic material.
The reader portion is typically formed of a bottom reader shield, a top reader shield and a magnetoresistive (MR) sensor positioned between the bottom and top reader shields. The top shield is the shield closest to the writer portion. Insulating layers are positioned between the MR sensor and the reader shields. The writer portion and reader portion are often arranged in a merged configuration in which a shared pole serves as both the top reader shield in the reader portion and a return pole in the writer portion.
A magnetic medium for perpendicular recording is generally formed of three layers: a medium layer having high perpendicular anisotropy, a nonmagnetic interlayer, and a soft magnetic underlayer (SUL) having high permeability. A perpendicular writer portion is positioned to write data in track on the magnetic medium, which is rotated at a high speed. The transducing head is supported over a surface of the magnetic medium by a thin cushion of air produced by the high rotation speed. This surface is the ABS referenced earlier.
In order to write to the magnetic medium, a time-varying electrical current, also known as a write current, is caused to flow through the conductive coils layers of the perpendicular writer. The write current produces a time-varying magnetic field through the main and return poles. The main pole and return pole assume opposite magnetic charges at any instant for a given write current, thus the magnetic field links from the main pole to the return pole, or vice versa. The magnetic medium is passed near the ABS of the transducing head at a predetermined distance such that a magnetic surface of the medium passes through the magnetic field. The main pole is generally the trailing pole of the main and return poles, thus the main pole is used to physically write the data to the magnetic medium. Accordingly, it is the main pole that defines the track width of the written data. More specifically, the track width is defined by the width of the main pole at the ABS.
The SUL of the magnetic medium essentially acts as a third pole of the writer, imaging the magnetic field emanating from the main pole. The magnetic field bridges the gap from the main pole to the SUL, passing through the medium layer, and then subsequently bridges the gap between the SUL and the return pole, again passing through the medium layer. The latter portion is known as the return path. Data is written to the magnetic medium as the magnetic field, having a magnetic field value larger than the coercive force of the magnetic medium, passes through the medium layer from the main pole. The magnetization in the magnetic medium is held in a direction substantially normal to the surface of the magnetic medium.
The return pole is substantially larger than the main pole at the ABS to help prevent the magnetic field from writing or erasing data on the return path. That is, the magnetic flux through the medium layer in the return path should not be concentrated sufficiently to overcome the coercive force of the medium. By making the return pole substantially larger than the main pole at the ABS, the magnetic flux density in the return path is decreased.
The reader portion of the transducing head functions to retrieve magnetically-encoded data stored on a magnetic medium. When the transducing head is placed near the magnetic medium, a resistance of the MR sensor fluctuates in response to a magnetic field emanating from written transitions in the magnetic medium. By providing a sense current through the MR sensor, the resistance of the sensor can be measured and used by external circuitry to decipher the information stored on the magnetic medium. The reader shields function to absorb any stray magnetic fields emanating from adjacent tracks on the magnetic medium or neighboring magnetic bits on the same track so that the MR sensor will read only information stored directly beneath it on a specific track of the magnetic medium.
In recent years, writer portion widths and reader portion widths have been decreased to accommodate ever-increasing areal densities of magnetic storage. Perpendicular recording allows for higher linear bit density as compared to longitudinal recording because the bits are written to the magnetic medium in a direction substantially normal to the surface of the medium, rather than substantially parallel to the surface of the medium as in parallel recording.
A perpendicular recording system requires a medium with a SUL of high permeability as a result large magnetic field appearing at a trailing edge of the return pole during the write process. The trailing edge of the return pole is the edge closest to the main pole. The large magnetic field at the trailing edge of the return pole results from the magnetic field concentrating itself at the trailing edge of the return pole during the return path. In addition, the trailing edge of other magnetic elements of the transducing head, such as the reader shields, may generate a large magnetic field, caused by stray magnetic fields emanating from the return path. The large magnetic field generated at the trailing edge of the return pole or the reader shield is generally known as the erasure field. The erasure field can be large enough to erase or write over previously written neighboring tracks on the magnetic medium by destabilizing the medium magnetization configuration or write over the previously written tracks by reorienting the previously defined magnetization pattern. The erasure field activity is generally known as “side-writing.” Transducing heads that reduce or minimize side writing are desirable. Thus, there is a need for a transducing head design which reduces side-writing.